Improvement in production of omicron, omicron-dialkyl-o, 2-pyrazinyl phosphorothioate



United States Patent Ofifice 3,091,614 Patented May ZS, 1963 3,091,614IMPROVEMENT IN PRODUCTION OF 0,0-DIAL- KYL-0,-2-PYRAZ1NYLPHOSPHOROTHIOATE Bernard Miller, Princeton, N.J., and Malcolm RobbinsForbes, New Rochelle, N.Y., assignors to American Cyanamid Company, NewYork, N.Y., a corporation of Maine No Drawing. Filed Jan. 9, 1962, 581'.No. 165,257

4 Claims. (Cl. 260-250) The present invention relates to a novel andimproved method for preparing phosphate esters of the general formulawherein R and R represent lower alkyl, such as methyl, ethyl, propyl,isopropyl and bntyl, and X, Y and Z each represent hydrogen, halogen,phenyl or a lower alkyl.

Compounds of the general formula given above and their preparation arefully described in US. 2,918,468, patented December 22, 1959. In thispatent a dialkyl phosphorochloridothioate of the formula is reacted withan alkali metal salt of a hydroxypyrazine of the formula alkalimetal-O-K X Z- LY N in an inert solvent and at a temperature in therange of about C. to about 100 C., preferably between 20 C. and 60 C. R,R, X, Y and Z in the latter two formulae have the same meaning givenabove in the product formula.

According to US. 2,918,468 the 0,0-dialkyl O-(2-pyrazinyl)phosphorothioates may also be prepared by reacting dialkylphosphorochloridothioate with the hydroxypyrazine in an inert solvent inthe presence of a hydrogen chloride acceptor, such as an alkali metal oran alkaline earth metal carbonate.

Suitable inert solvents according to US. 2,918,468 are water,dimethylformamide, dioxane, N-methyl-Z-pyrrolidone, acetonitrile,benzene, toluene, Xylene, the lower aliphatic monohydric alcohols,ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone,methyl benzyl ketone and cyclohexanone, and aliphatic esters, such asethyl acetate, 2-ethylhexyl acetate, methyl propionate, ethyl butyrateand isopropyl butyrate.

Pursuant to the instant discovery it has been found that verysignificant increases in yields and substantially purer products may beachieved by modifying the process of US. 2,918,468. Pursuant to theinstant invention an alkali metal salt of a'hydroxypyrazine of theformula alkali metal-O is brought into reactive contact with a dialkylphosphorochloridothioate of the formula at a temperature in the range of10 C. to about 100 C., preferably 60 C. to 'C., and in the presence ofcuprous chloride (Cu Cl catalyst. Ketones of the type described above,such as methyl isobutyl ketone, and so on, are the preferred solvents.R, R, X, Y and Z have the meanings given above.

Further, it has been discovered pursuant to the present discovery thatoptimum results are achieved when cuprous chloride particulates of aparticular size are employed. At least of the particulates should becapable of passing through a ZOO-mesh Tyler screen. It is alsopreferable to maintain an excess of the alkali metal salt of ahydroxypyrazine, based upon the dialkyl phosphorochloridothioatereactant, throughout the reaction. An excess up to 20%, preferably from10% to 15%, is maintained.

Surprisingly enough, product purity in the neighborhood of 95 percent byweight and greater is realized as a result of the instant discovery. Thereason for this improvement is not known. Furthermore, it is verysurprising that the copper in cuprous chloride does not, as a potentialcontaminant, deleteriously affect the pesticidal activity of theproducts herein prepared. One would expect problems, such asphytotoxicity, etc.

On the contrary, beneficial results have been achieved by virtue of thepresence of only minor amounts of copper in the final product. Forinstance, whereas petroleum ether insoluble tars in the range of 10 to20 percent by weight heretofore accompanied the production of theproducts of the present invention, no cuprous chloride being used tocatalyze the process, the instant discovery has reduced the amount ofthese tars to 1 percent by weight, or less.

The products as prepared heretofore had a tendency to solidify uponstanding. Using the process of the present invention, however, much morestable products are achieved. The exact reason for this is not fullyunderstood but it is known that the use of cuprous chloride as taughtherein makes the difference.

The cuprous chloride particulates employed for optimum results generallyhave a surface area in the range of 0.5 square meter per gram to 1.0square meter per gram (m. /gm.), prefer-ably about 0.6 to 0.8 squaremeter per gram. I

It should be noted that up to 20 grams of Cu cl per mole of dialkylphosphorochloridothioate reactant may be used to achieve the verydesirable results of the present discovery, preferably about 15 grams ofCu Cl per mole of dialkyl phosphorochloridothioate. Any practicalamount, however, is beneficial.

The present invention will best be understood from the followingexample:

EXAMPLE I 0,0-diethyl-O-(2-pyrazinyl)phosphorothioate is prepared from'0,0-diethylphosphorochloridothioate and sodium pyrazinola-te, 15%excess, in the presence of 15 grams of cuprous chloride per mole of0,0-diethylphosphorochloridothioate, and in a methyl isobutyl ketonemedium. The Cu Clparticulates, over 95 of which could pass through aZOO-mesh (Tyler) screen, had an average surface area of 0.7 square meterper gram (m /gm). The 0,0-diethylphosphorochloridothioate is added overa one hour period at 80 C. followed by a hold period of 1.5 hrs. at 80C. The reaction mixture is cooled to 25 C. and filtered to remove NaCland other insolubles, sodium pyrazinolate and cuprous salts. Theresulting filter cake is washed to remove occluded product. The filtrateis washed twice with Water and then stripped in a low residence timeevaporator to remove the solvent.

formula N alkali metal-O 1X zl Y said reaction being made to take placein the presence of Table I R o s Percent o 01 R o s excess ui z II Alkahmetal X of Temp., catalyst Solv. II N E /POO1 (B) 0 PO X x. No. R-O overGms. per Surface R0 (A) mole (A) area Y (A) (B) (ma/ N Alkali R R metalX Y Z (C) II. Ethyl Ethyl Na H 12 70 15 0 8 Methylethyl0,0-diethyl-O-(2-pyraketone. zitnyDphosphorothioae. IIL.-- Methyl.-.Mcthy1- K H H H 10 90 18 0 5 Methyl benz- 0,0-dlrnethyLO-(2- yl ketone.pyrazinyl) phosph0rothioate.

V Butyl Butyl Na 01 H H 5 85 1.0 Methyl lsobu- 0,0-dibutyl-O-(G- tylketone. chloro-2-pyrazinyl)- phosphorothioate.

V PrQpyL--. Pr0pyl Na H C H H 13 55 13 0.6 Acetone 0,0-dipropyl-O-(5-phenyl-Z-pyrazinyD- phosphorothioate.

VI Ethyl Ethyl Na C6115 0011 H 15 75 19 0 6 Gyclohexa-0,0-diethy1-O-(5,6-

none. phenyl-2-pyrazinyD- phosphorothioate.

VII-.. Methyl.-- Methy1. K Br H H 15 75 11 0.7 Methyl isobu-0,0-dimethy1-O-(6- tyl ketone. brorno-2-pyrazlnyl) phosphorothioate.

VIIL. Butyl Butyl Na K E 0 H; 18 14 0 8 tert-Butanol..-0,0,dibutyl-O-(3-pheny1 2-pyrazinyD-phosphorothioate.

IX.. Isopropyl. IsopropyL. Na (32H; 02115 H 20 13 0.6 do0,0-diisopropy1-O-(5,6-

diphenyl-2-pyrazlnyD- phosphorothioate.

X.- Ethyl"--- Ethyl K CH; OH; 01 9 80 13 0.9 Methyl isobu-0,0-diethyl-O-(3-chlorotyl ketone. %i1pyr?zinyl)phosphoroloa e.

XI do do. Na 01 Cl 01H: 11 75 6 0.7 Ethylacetate"0,0-diethyl-O-(3-ethy1- 5,6-dichloro-2-pyrazinyDphosphorothioate XII-.-Propy1. PropyL-.. Na H H iso-CrHv 3 5O 9 0 7 Methyl isobu-0,0-dipropyl-O-(3-isotyl ketone. propyl-2-pyrazinyD- phosphorothioate.

The compounds of the present invention are highly active insecticidesand acaricides and may be used as sprays in organic solvents, asemulsions in Water or other non-solvents, or on solid carriers, such astalcs, clays, diatomaceous earths and the like.

Clearly, the instant discovery encompasses numerous modifications withinthe skill of the art. Consequently, while the present invention has beendescribed in detail with respect to specific embodiments thereof, it isnot intended that these details be construed as limitations upon thescope of the invention, except insofar as they appear in the appendedclaims.

We claim:

1. A method of preparing a phosphate ester of the formula an inertsolvent and in the presence of up to about 20 grams cuprous chloride (CuCl catalyst per mole of dialkyl phosphorochloridothioate, and recoveringthe re- 45 sulting phosphate ester of the general formula above,

R, R, X, Y and Z in the reactant formulae having the same meaning giventhem in the product formula, supra.

2. The process of claim 1 wherein the alkali metal salt of ahydroxypyrazine reactant is present, throughout the reaction, in excessrelative to the dialkyl phosphorochlori- 0 duced.

References Cited in the file of this patent UNITED STATES PATENTS 52,784,207 Geoghegan et a1 Mar. 5, 1957 2,918,468 Dixon Dec. 22, 1959FOREIGN PATENTS 713,278 Great Britain Aug. 11, 1954

1. A METHOD OF PREPARING A PHOSPHATE ESTER OF THE FORMULA